1. Field of the Invention
The present invention relates to a method for manufacturing a piezoelectric actuator capable of adjusting the shape thereof and to a piezoelectric actuator adaptable to the method for manufacturing a piezoelectric actuator and formed unitarily with a support to have excellent mechanical strength.
2. Description of Related Art
Cell phones have been spreading globally. However, they have not yet been standardized. Therefore, each cell phones require a RF (Radio Frequency) circuit in accordance with the standard (frequencies) of each country in the world. Therefore, it is necessary to change specification depending on each country or to mount a plurality of RF circuits in order to respond to all the standards. This causes cost increase, and, particularly in the latter case, it becomes an obstacle to miniaturization.
In order to solve such a problem, in recent years, a variable capacitor has been proposed. For a variable capacitor, there are drive systems such as a piezoelectric drive type, an electrostatic drive type, and an electromagnetic type drive type. Generally, an electrostatic drive type is employed be cause of a simple structure and easy production. However, it needs a high drive voltage and has a narrow variable capacity as the points to be improved. In addition, an electromagnetic drive type has high power consumption.
Therefore, in recent years, development of a piezoelectric drive type variable capacitor has been having high expectations. Incidentally, prior art documents are JP-A-2008-005642, JP-A-2001-320103, and “Phenomenological Dielectric”, 24th edition, Pages 153 to 188, issued by the Institute of Electrical Engineers of Japan.
However, in a conventional piezoelectric drive type variable capacitor, the interval between two capacitor electrodes is not fixed due to remnant strain in the production process, and the two capacitors may fail to come close or draw apart from each other while maintaining parallelism. In such a case, the relation between the displacement amount of the piezoelectric actuator and capacity of the capacitor becomes unstable, and two capacitor electrodes are brought into contact with each other, thereby decreasing the width of the variable capacity.
FIG. 3 is a schematic view showing a conventional piezoelectric drive type variable capacitor showing a condition where the piezoelectric actuator of the variable capacitor is driving. In the variable capacitor 30 shown in FIG. 3, in a piezoelectric actuator 31 having a bimorph type actuator portion 38 having an end portion fixed to a support 39, a capacitor electrode 36 is disposed on one surface of the actuator portion 38, and another capacitor electrode 33 is disposed so as to face the capacitor electrode 36. In the variable capacitor 30, the actuator portion 38 of the piezoelectric actuator 31 is transformed in the directions of the arrows (in FIG. 3) to control the distance between the capacitor electrodes 33 and 36, and thereby the electrostatic capacity generated between them can be changed. However, as shown in FIG. 3, in a conventional variable capacitor 30, since the actuator portion 38 of the piezoelectric actuator 31 is transformed to have an arcuate shape, the capacitor electrodes 33 and 36 fail to come close or draw apart from each other while maintaining parallelism, and the capacitor electrodes 33 and 36 are brought into contact with each other in some cases.